The light receiving member used for image formation has a light receiving layer made of a photoconductive material. This material is required to have characteristic properties such as high sensitivity, high S/N ratio [ratio of light current (Ip) to dark current (Id)], absorption spectral characteristic matching the spectral characteristic of electromagnetic wave for irradiation, rapid optical response, appropriate dark resistance, and non-toxicity to the human body at the time of use. The non-toxicity at the time of use is an important requirement in the case of a light receiving member for electronic photography which is built into an electrophotographic apparatus used as an office machine.
A photoconductive material attracting attention at present from the standpoint mentioned above is amorphous silicon (A-Si for short hereinafter). The application of A-Si to the light receiving member for electrophotography is disclosed in, for example, German Laid-open Pat. Nos. 2746967 and 2855718.
FIG. 2 is a schematic sectional view showing the layer structure of the conventional light receiving member for electrophotography. There are shown an aluminum support (201) and a photosensitive layer of A-Si (202). This type of light receiving member for electrophotography is usually produced by forming the photosensitive layer 202 of A-Si on the aluminum support 201 heated to 50.degree..about.350.degree. C., by deposition, hot CVD process, plasma CVD process, or sputtering.
Unfortunately, this light receiving member for electrophotography has a disadvantage that the sensitive layer 202 of A-Si is liable to crack or peel off during cooling subsequent to the film forming step, because the coefficient of thermal expansion of aluminum is nearly ten times as high as that of A-Si. To solve this problem, there was proposed a photosensitive body for electrophotography which is composed of an aluminum support, an intermediate layer containing at least aluminum, and a sensitive layer of A-Si. (Japanese Patent Laid-open No. 28162/1984) The intermediate layer containing at least aluminum relieves the stress arising from the difference in the coefficient of thermal expansion between the aluminum support and the A-Si sensitive layer, thereby reducing the cracking and peeling of the A-Si sensitive layer.
The conventional light receiving member for electrophotography which has the light receiving layer made of A-Si has been improved in electrical, optical, and photoconductive characteristics (such as dark resistance, photosensitivity, and light responsivity), adaptability of use environment, stability with time, and durability. Nevertheless, it still has room for further improvement in its overall performance.
For the improvement of image characteristics, several improvements have recently been made on the optical exposure unit, development unit, and transfer unit in the electrophotographic apparatus. This, in turn, has required the light receiving member for electrophotography to be improved further in image characteristics. With the improvement of images in resolving power, the users have begun to require further improvements such as the reduction of uneveness (so-called "coarse image") in the region where the image density delicately changes, and the reduction of image defects (so-called "dots") which appear in black or white spots, especially the reduction of very small "dots" which attracted no attention in the past.
Another disadvantage of the conventional light receiving member for electrophotography is its low mechanical strength. When it comes into contact with foreign matters which have entered the electrophotographic apparatus, or when it comes into contact with the main body or tools while the electrophotographic apparatus is being serviced for maintenance, image defects occur or the A-Si film peels off on account of the mechanical shocks and pressure. These aggravate the durability of the light receiving member for electrophotography.
An additional disadvantage of the conventional light receiving member for electrophotography is that the A-Si film is susceptible to cracking and peeling on account of the stress which occurs because the A-Si film differs from the aluminum support in the coefficient of thermal expansion. This leads to low yields in production.
Under the circumstances mentioned above, it is necessary to solve the above-mentioned problems and to improve the light receiving member for electrophotography from the standpoint of its structure as well as the characteristic properties of the A-Si material per se.